Check to see if the AUX cord is firmly connected to both devices. If this does not work and are only two rings, your cord is not compatible. If there are three rings, replace the auxiliary cord. If this does not work, the problem may be with the auxiliary cord jack and you may need to replace it.

How can I connect my iPhone to my aux cable in my car?

Connect the cable to your iPhones headphone jack and the auxiliary port on the stereo. Plug one end of the audio auxiliary cable to the headphone port of your iPhone. Take the other end of the cable and plug it to the auxiliary port on the car stereo. Set your car stereo to Auxiliary mode.